The acrylic acid adducts of various epoxide materials have been described in various prior art patents. For example, U.S. Pat. No. 3,301,743 describes the acrylic acid adducts of epoxidized phenol-formaldehyde novolac resins, and an acrylic acid adduct of a diglycidyl ether of Bisphenol A is described in U.S. Pat. No. 3,317,465. Acrylic acid adduct of soy bean oil compositions is disclosed by Ackerman et al in U.S. Pat. No. 3,713,864. These patents describe compositions in which the acrylic groups are linked to the epoxy backbone material by an ester group, but fail to describe the ether linkage which results from the hydroxy-epoxide reaction and the variations available therefrom.
Among the requirements for the successful preparation of a radiation curable composition is a facile synthesis of the composition and the need for a minimum of inhibitor concentrations. Whereas the acrylic acid derivatives can be prepared, they often require extended heating, depending on the catalyst employed. Extended heating at 100.degree. C. or greater can lead to the vapor phase polymerization of acrylic acid creating hazards and other synthetic difficulties. If the synthesis is not 100% complete, residual acrylic acid will be incorporated into the cured film which in certain coating applications is very undesirable.
The synthesis of the oligomers of the present invention is extremely rapid and fully controllable when carried out in the fashion disclosed in this specification. Further, residual reactants are hydroxyl bearing constituents and are less objectionable when incorporated into the cured film. It is not uncommon to use hydroxyl compounds as reactive diluents for radiation curing systems. Lastly, the hydroxyl compounds are considerably less volatile than acrylic or methacrylic acid, thus minimizing vapor phase polymerization, odors and the like.
The novel products of the present invention offer superior radiation response with respect to film properties of coatings when compared to the acrylic acid-epoxide reaction products. The increased radiation response can be attributed to the multiplicity of radiation curable sites which can be achieved with the compositions of the present invention. Multiplicity of radiation curable sites are not possible with acrylic acid adducts mentioned in the prior art. The reaction of the hydroxy group with the epoxide group produces an ether linkage and it is postulated that the ether-type linkage has superior radiation response as compared to the ester-type linkage which results from an epoxide-acid reaction. The ether group is believed to affect the curing reaction [ref. Sonntag, C., Schuchmann, H., Schomburg, G., Tetrahedron 28 (16) 4333-9 (1972)]. Thus, increased line speeds are possible using the oligomers of the present invention. By proper selection of the hydroxyl vinyl compound, film flexibility can also be controlled without any sacrifice in the rapid radiation response. As a further manifestation of the ether linkage activity, quite surprisingly, is the observation that adhesion is enhanced with the compositions of the present invention, as compared to acrylic acid adducts.